The invention relates to radioactive ruthenium radiation sources having a dose rate of at least 1.5 Gy/min at a distance of 2 mm (water), comprised of an activity carrier and an enclosure for said carrier made of a body-compatible material, the carrier having electrodeposited thereon a multilayer system of metals and/or alloys, wherein at least two layers consist of ruthenium-106, and wherein inactive intermediate layers of other metals or alloys are present between the radioactive ruthenium layers.
The activity carrier is enclosed in a body-compatible material such as metal or plastic. Enclosing the activity carrier can be performed by filling into a capsule and subsequent sealing, or by electrodepositing a cover layer made of e.g. hard gold.
The electrodeposition of non-radioactive ruthenium coatings on various substrates is well-known from the literature. A variety of electrolytes including most various additives have been described for this purpose. What is involved is the deposition of well-adhering coatings which are sufficiently thick and nevertheless glossing and free of cracks.
Thus, in the article by G. S. Reddy et al., "Electro-deposition of Ruthenium", in TIMF 47 (1969), pp. 187-193, for example, the anionic ruthenium complex (NH.sub.4).sub.3 [Ru.sub.2 NCl.sub.8 (H.sub.2 O).sub.2 ] has been described as electrolyte, by means of which stable baths and glossing ruthenium coatings are obtained.
The DE-OS 22 61 944 concludes that coatings produced using such baths exhibit gloss only up to a thickness of about 2-3 .mu.m, and that surface cracks will occur with increasing thickness. Therefore, this document suggests a modified electroplating bath, by means of which ruthenium layers 5 .mu.m in thickness are said to be obtained. This bath likewise includes a complex ruthenium compound having the Ru--N--Ru nitrogen bridge (produced from the above-mentioned electrolyte), but is free of halogen, includes at least 1.5 g/l of sulfate ions, and has a pH value of 4 at maximum.
However, because the electrodeposition of ruthenium on copper, nickel or nickel-iron alloys does not proceed satisfactorily under acidic conditions for uses in electric engineering, and therefore, the substrate must first be coated with a thin layer of gold or another suitable material, some prior art documents have also described alkaline or neutral baths including complex ruthenium compounds having an Ru--N--Ru nitrogen bridge, e.g. in GB 1,520,140 of 1978 (alkaline) and in EP 0,018,165 of 1980 (addition of oxalic acid, pH value 7, diaphragm cell).
In context with the deposition of radioactive ruthenium layers, the French patent specification FR 1,206,612 (filed 1956) has been the first to be known from the literature. It essentially describes non-radioactive electrolytic depositions based on an electrolytic bath comprised of ruthenium(IV) chloride solution at 95-100.degree. C. A coating of 4 mg/cm.sup.2 is described, corresponding to a layer thickness of about 3 .mu.m. Furthermore, it is noted in this written specification that a layer thickness of up to 8 mg/cm.sup.2 would be possible when using this method. This would correspond to a layer thickness of about 6 .mu.m. The problems with crack formation at layer thicknesses above 3 .mu.m, which are well-known from the literature, have not been mentioned in this early document. Finally, this patent specification concludes that this method would also allow the production of radioactive sources but fails to demonstrate in which way such sources with sufficiently stable layers for medical uses could be obtained.
In contrast, a practical use of radioactive ruthenium is described in "Isotopenpraxis", Vol. 2, No. 4 (1966), pp. 189-193, wherein a deposition from highly diluted, inactive ruthenium(III) chloride solutions with addition of 30-70 .mu.Ci of .sup.106 Ru as tracer has been performed.
However, it was found that the deposition described therein does not allow mechanically stable layers of significant thickness to be obtained, and that uniform distribution of activity on the preparations could only be achieved in excessively slow depositions. Such sources merely have limited usefulness for medical applications.
Marketed ruthenium radiation sources for ophthalmologic purposes are produced by electrolytic deposition of ruthenium from commercially available radioactive ruthenium(III) chloride solutions. The thin layers obtained thereby, having dose rates of from 0.1 to 0.5 Gy/min, are sufficient for using this radiation source as eye applicator in eye tumor treatment. However, these radiation sources are unsuitable in the treatment of vascular anomalies because they do not have the required dose rate due to the fact that thin layers can only be achieved.